Crystal structures and microwave dielectric properties of low-firing Ca5Zn4-xMgxV6O24 ceramics

Ca5Zn4-xMgxV6O24 (x = 0-3) microwave dielectric ceramics with low sintering temperature were synthesized via the conventional solid-state reaction. Effects of the substitution of Mg2+ for Zn2+ on crystal structures and microwave dielectric properties were investigated. XRD and Rietveld refinement showed the solid solution single phase formed when 0 <= x <= 2, but a few ZnO was observed when x = 3. Meanwhile, the lattice parameters were found to decrease monotonously with Mg content increasing. The vibration modes of Raman were confirmed and the relationship with microwave dielectric properties was analyzed. Appropriate substitution of Mg2+ improved the packing fraction, the cation ordering degree, and the Y-site bond valence, contributing to high Q x f and low vertical bar tau(f) vertical bar. However, the epsilon(r) reduced with the increasing content of Mg2+ due to the decrease of ion polarizability. Finally, the best microwave dielectric properties were achieved at x = 2 with sr = 11.0, Q x f = 66,365 GHz (at 10.0 GHz), and tau(f) = 80.4 ppm/degrees C.